Computer disk drives store information on magnetic disks. Typically, the information is stored on each disk in concentric tracks, or cylinders, that are divided into sectors. Information is written to and read from a disk by a transducer that is mounted on an actuator arm capable of moving the transducer radially over the disk, allowing the transducer to be located in proximity to different cylinders. The disk is rotated by a spindle motor at high speed which allows the transducer to access different sectors on the disk.
A diagrammatic representation of a conventional disk drive, generally designated 10, is illustrated in FIG. 1. The disk drive comprises a disk 12 that is rotated by a spindle motor 14. The spindle motor 14 is mounted to a base plate 16. An actuator arm assembly 18 is also mounted to the base plate 16. The disk drive 10 also includes a cover (not shown) that is coupled to the base plate 16 and encloses the disk 12 and actuator arm assembly 18.
The actuator arm assembly 18 includes a flexure arm 20 attached to an actuator arm 22. A transducer 24 is mounted near the end of the flexure arm 20. The transducer 24 is constructed to magnetize the disk 12 and sense the magnetic field emanating therefrom. Attached to the end of the flexure arm 20 is a ramp tab 25, which engages with a ramp 26 when the actuator arm assembly 18 is parked, as will be described in more detail below. It should be noted that ramp 26 may be located either at the inner diameter of the disk 12, or at the outer diameter of the disk 12. The actuator arm assembly 18 pivots about a bearing assembly 27 that is mounted to the base plate 16.
Attached to the end of the actuator arm assembly 18 is a magnet 28 located between a pair of coils 30. The magnet 28 and coils 30 are commonly referred to as a voice coil motor 32 (VCM). The spindle motor 14, transducer 24 and VCM 32 are coupled to a number of electronic circuits 34 mounted to a printed circuit board 36, which comprise the control electronics of the disk drive 10. The electronic circuits 34 typically include a read channel chip, a microprocessor-based controller and a random access memory (RAM) device.
The disk drive 10 typically includes a plurality of disks 12 and, therefore, a plurality of corresponding transducers 24 mounted to flexure arms 20 for the top and bottom of each disk surface. However, it is also possible for the disk drive 10 to include a single disk 12 as shown in FIG. 1.
The flexure arm 20 is manufactured to have a bias such that if the disk 12 is not spinning, the transducer 24 will come into contact with the disk surface 12. When the disk is spinning, the transducer 24 typically moves above, or below, the disk surface at a very close distance, called the fly height. This distance is maintained by the use of an air bearing, which is created by the spinning of the disk 12 surface such that a boundary layer of air is compressed between the spinning disk 12 surface and the transducer 24. The flexure arm 20 bias forces the transducer 24 closer to the disk 12 surface, while the air bearing forces the transducer 24 away from the disk 12 surface. Thus, the flexure arm 20 bias and air bearing act together to maintain the desired fly height when the disk 12 is spinning.
It will be understood that if the disk 12 is not spinning at a high enough RPM, the air bearing produced under the transducer 24 may not provide enough force to prevent the flexure arm 20 bias from forcing the transducer 24 to contact the disk 12 surface. If the transducer 24 contacts an area on the disk 12 surface that contains data, some of the data may be lost. To avoid this, the actuator arm assembly 18 is generally positioned such that the transducer 24 does not contact a data-containing area of the disk 12 when the disk 12 is not spinning, or when the disk 12 is not spinning at a high enough RPM to maintain an air bearing.
In a load/unload (L/UL) drive, as illustrated in FIG. 1, the ramp tab 25 located at the end of the flexure arm 20 is parked on a ramp 26 when the disk is not spinning. Parking the ramp tab 25 on the ramp 26 prevents the bias from the flexure arm 20 from forcing the transducer 24 into contact with the disk 12 surface when the disk 12 is not spinning, thus helping to avoid data loss.
With reference now to FIG. 2, a diagrammatic representation illustrating a side view of a simple ramp 26 is now described. The ramp 26 has an upper ramp portion 50 and a lower ramp portion 54. Thus, when the ramp tab 25 engages the upper or lower ramp portion 50, 54, it moves along the ramp and into a parked position. Located at the end of the ramp 26 farthest away from the disk 12 is a crash stop 58. The crash stop 58 acts to prevent the actuator arm assembly 18 from traveling beyond its range of motion, which can cause damage to the actuator arm assembly 18. The crash stop 18 is typically made of a material, such as plastic, which can absorb some amount of energy from an impact.
As mentioned above, when performing read and write functions, the transducer 24 is positioned above the track associated with the data to be read or written. When a disk drive 10 receives a request to access a certain track, it must move the actuator arm assembly 18 and transducer 24 to the associated track. A servo control system is generally used to control the VCM 32 and locate the transducer 24 above the appropriate track. Servo control systems generally perform two distinct functions: seek control and track following. The seek control function comprises controllably moving the transducer 24 from an initial track position to a target track position. In this regard, the servo control system receives a command from a host computer that data is to be written to or read from a target track of the disk, and the servo system proceeds to move the transducer 24 to the target track from the track where it is currently located. Once the transducer 24 is moved sufficiently near the target track, the track following function is performed to center and maintain the transducer 24 on the target track until the desired data transfer is completed.
When performing a seek function, it is desirable to reduce the amount of time it takes for a transducer 24 to move from its starting track to the target track. Average seek time is a measure of how fast, on average, a disk drive takes to move a transducer 24 to a target track from a starting track after a command is received from a host computer to access the target track. Because speed is a very important attribute in computer systems, average seek time is generally used as one of the indications of the quality or usefulness of a disk drive. Therefore, it is highly desirable to reduce the average seek time of a disk drive as much as possible.
When performing a seek function, the servo system generally moves the transducer 24 according to a seek profile. A typical seek profile includes an acceleration portion and a deceleration portion, with the transducer 24 reaching a peak velocity at the end of the acceleration portion. The length of the seek is defined as the distance between the starting track and the target track. For relatively long seek lengths, the actuator arm assembly 18, and transducer 24, may reach a peak velocity, and coast for a period of time at a relatively constant velocity prior to decelerating. Likewise, for relatively short seek lengths, the velocity of the transducer 24 may not reach the peak velocity prior to decelerating. Thus, the shape of the seek profile depends upon the seek length, and may or may not include a coasting portion where the velocity of the transducer 24 reaches the peak velocity.
As mentioned above, in normal operation, when a disk drive 10 is shut down, the control electronics 34 operate to position the actuator assembly 18 such that the transducer 24 does not contact the data containing portion of the disk 12 surface when the disk 12 stops spinning. In certain situations, however, a disk drive 10 may lose power while a transducer 24 is flying over the disk 12 surface where customer data is stored. Such situations may, for example, include a loss of power to the computer system containing the disk drive, a power supply malfunction within the computer or disk drive, or an inadvertent disconnect of the power to the disk drive prior to the drive being shut down. In order to reduce the chances of data being lost when a power failure occurs, methods and apparatuses have been developed which position the actuator arm assembly 18 such that the transducer 24 will not contact the data-containing portion of the disk 12 surface. One conventional method for parking the transducer 24 is to actuate a retract circuit to place the ramp tab 25 of the actuator arm assembly 18 on the ramp 26, thus clearing the transducer 24 of the data containing area of the disk 12.
The retract circuit is typically contained within the electronic circuits 34, and is generally powered using the back electromotive force (BEMF) generated from the windings of the spindle motor 14. When a power loss is detected, an automatic park cycle is initiated, and the retract circuit is electrically connected to the windings of the spindle motor 14. The retract circuit actuates the VCM 32 and parks the actuator arm assembly 18 to clear the transducer 24 from the area of the disk 12 surface which contains customer data.
However, in certain situations, the loss of power may occur while the disk drive 10 is performing a seek function. If the actuator arm assembly 18 is seeking toward the ramp 26 at a high enough speed, the BEMF from the spindle motor windings may not generate enough voltage to slow the actuator arm assembly 18 down significantly, and the ramp tab 25 may load onto the ramp 26 at a high rate of speed (see FIGS. 1 and 2). If the actuator arm assembly 18 is traveling at a sufficiently high velocity, the ramp tab 25 may hit the crash stop 58, bounce back off of the crash stop 58, travel back off of the ramp 26 and over the disk 12 surface. In such a situation, the actuator arm assembly 18 may be in an uncontrolled state, which may cause the transducer 24 to come into contact with the disk 12 surface, and potentially damage the disk 12 surface which can result in loss of customer data. Such an event may also cause damage to the transducer 24. Furthermore, if the ramp tab 25 hits the crash stop 58 at a high velocity, it may cause mechanical damage to the crash stop 58 and/or the ramp tab 25.
A common solution to this problem has been to derate seek profiles to ensure that the actuator arm assembly 18 and transducer 24 do not travel at a velocity high enough for such a situation to occur. This is typically achieved by creating a seek profile which limits the velocity at which the actuator arm assembly 18 is allowed to travel. While this solution reduces instances of the ramp tab 25 bouncing off of the crash stop 58, it also results in a seek velocity profile which has an increased seek time compared to a seek velocity profile which does not limit the actuator arm assemblyl8 and transducer 24 velocity.
Another solution has been to use a disk having a glass surface which is more robust and less susceptible to damage and, therefore, less susceptible to data loss. However, glass media can add additional expense to the manufacture of the disk drive compared to the more common aluminum media and, thus, can result in a higher cost to the consumer. Furthermore, the glass layer makes magnetic recording more difficult.
Still another solution is to ensure that the power to the disk drive is not removed prior to a controlled disk drive shut down. This solution is common in mobile platforms where a battery is available to supply power to the computer system rather than, or in addition to, a power supply connected to an external power source. In such a platform, even if a user disconnects the external power supply, the battery is still available to provide power to the system. Additionally, the power switch in such a system typically is connected to circuitry which performs a controlled shut down of the system if it is pressed by a user. However, in non-mobile platforms adding a battery increases overall costs.
In yet another solution, a latch may be provided which engages the actuator arm. The use of a latch to secure the actuator arm on the ramp is well known in the art. Using the latch to engage the actuator arm when it is traveling at a relatively high velocity can prevent the transducer from bouncing off of the crash stop and reloading onto the disk. However, such a latch is more complex to design and manufacture, again resulting in additional cost to manufacture the disk drive.
Accordingly, there is a need to develop a method and apparatus for use during a power loss to a disk drive which: (1) reduces the instances of the actuator arm assembly bouncing off the crash stop and over data containing areas of the disk when power is lost to the disk drive, (2) has a reduced effect on average seek time as compared to systems which limit transducer velocity on all seeks, and (3) is able to be implemented largely in firmware thereby requiring little or no additional hardware modifications over existing designs.